Carburetor



P. F. ADAIR April 29, .1947.

CARBURETOR Filed Oct. 14, 1944 52m Oh HIP-.53

v INVENTOR.

H01 fi'Aam NEYS Patented *Apr. 29, 1947 -UNITED STATES PATENT v OFFICE (u mimmrroa 1 Paul F. Adair, Dayton, Ohio Application October 14, 1944, Serial No. 558,706

Claim's. (01. 261-69) (Granted under the act of March 3, 1883, as

The invention described herein may be manufactured and used by or for the Governmentfor I governmental purposes, without the payment to meof any royalty thereon.

The present invention is related to carburetors for internal combustion engines, and particularly to pressure type carburetors suchasare I in current use on aircraft engines, in which'the fuel is injected into the stream of combustion air flowing to the engine under a pressure greater 1 than that of the air with which it is mixed.

It is an object of the present invention to provide an improved carburetor of.the type described,

- amended April 30, 1928; 370 o. G. 757) 2 cases the supercharger may be upstream from the inlet l2, or two superchargers may be used, one in each place.

The Venturi restriction l4 produces a pressure differential between the inlet l2 and the throat of the venturi which varies substantially in accordance with the square of the velocity of the air passing thru the venturi. Since the cross-sectional area of the venturi is constant, this pres- Another object is to provide, in a carburetor including a main fuel flow controlling valve and a pilot valve for regulating the main valve in response to the unbalancebetween air and fuel flows, an improved pilot valve construction such that the pilot valve is not affected by fuel pressure changes directly from its own operation, but only by fuel pressure changes resulting from operation of the main valve. 7 a

A further object of the present invention is to provide an improved carburetor including a fuel regulator unit which is interchangeable between different sizes of carburetors.

' Another object of the present invention is to provide an improved carburetor of a simplified and compact construction, using a minimum number of. parts.

Other objects and advantages of the present invention will become apparent from a consideration of the appendedspecification, claims and drawing, in which The single figure represents, somewhat diagrammatically, a carburetor for an internal com- 'bustion engine embodying the principles of my invention;

Referring to the drawing, there is shown a carburetor including an air conduit l0. Air enters the conduit H] at an inlet I2 and flows thru a Venturi restriction l4, past a throttle l6 and a fuel discharge nozzle Hi to an outlet 20. A supercharger may be placed between the outlet 20 and the intake manifold of the engine upon sure differential may be taken as a measure of the volume of air flowing thru the passage per unit time. 1

The pressure diflerential set up by the venturi I4 is utilized to create a flow of air thru a secondary air passage. The air enters this secondary air passage thru a plurality of tubes 22, whose ends are open to receive the impact of the entering air. In the secondary air passage, the air flows from the tubes 22 thru a passage 24 interconnecting all the tubes, a conduit 26, a fixed restriction 28, a conduit 30, past a valve 32 into a chamber 34, and then thru a conduit 36 to the throat of venturi l4.

-,The valve 32 is operated by a sealed bellows 38 mounted in the chamber 34. The bellows 38 is fixed at one end, so that the position of. the free end, to which valve 32 is attached, varies in accordance with the air pressure in the chamber 34. Bellows 38 is preferably filled with nitrogen or some other suitable temperature responsive fluid, so that the position of valve 32 varies not only with the pressure but also with the temperature of the air in the chamber 34, and hence with the density of that air.

The pressure differential produced by venturi I4 is a. measure of the volume of air flowing per unit time, as previously explained. Since it is desired to obtain a measure of the mass of air flowing per unit time rather than the volume, it is necessary for the metering apparatus to correct variations in. air density. This is accomplished by the valve 32 and bellows 38. The valve 32 is moved toward open position as the air density increases and toward closed'position as the air density decreases.

If the volume of air flowing per unit time thru the air conduit i0 remains constant and its den- .that the pressure drop across the restriction 28 is decreased to compensate for the decrease in density. The pressure drop across orifice 28 is H8 toward closed position.

3 thereby made to measure the mass of air flowin per unit time to the air conduit III.

A pressure meter, generally indicated at 40, includes a casing 42 whose interior is divided by two rigid transverse partitions 44 and 46. The space inside casing 42 above the partition 44 is further divided by a flexible diaphragm 48 into expansible chambers 50 and 52. The space between partitions 44 and 46 is divided by a flexible diaphragm .54 into expansible chambers 56 and 58. A valve stem 60 is attached at its center to the diaphragms 48 and 54 and extends thru central apertures in the partitions 44 and 56 into a valve chamber 52 below partition 46. The stem 60 carries at its lower enda pilot valve 64 which controls the flow of fuel into the valve chamber 62. Fuel flows freely out of the chamber 52 thru a conduit 56 leading to the air conduit II). A spring 65 biases the valve 54 in an opening direction.

Fuel enters the carburetor from a. fuel pump (not shown) or other source of fuel'under superatmospheric pressure. It flows thru a conduit 68, a mixture control unit generally indicated at 10, a jet system I2, an idle valve mechanism 14, a conduit I5, a flow regulator I8, and aaconduit 80 to the fuel discharge nozzle I8.

The mixture control unit 1.0 includes a disc valve 82 fixed on a shaft 84. The disc valve 82 controls the flow of fuel thru ports opening into conduits 85 and 88 which lead into thelet system 12. When the disc valve 82 is in the position illustrated in full lines in the drawing, fuel can flow to the jet system only thru the conduit 88. This is known as the lean" position of the mixture control I0. When the disc valve 82 is in the dotted line position shown in the drawing, the fuel can flow thru both the conduits 85 and 88. The dotted line position is termed the "rich position of the mixture control. The disc 84' can also be moved to a "cut-off position wherein it cuts off the flow of fuel thru both conduits and f 4 conduit I24 is controlled by valve 64. The chamber II4 receives fuel from the conduit 16 and is an inlet chamber for the valve II8.

For any given position of the mixture control unit III and of the valve 94, the fuel pressure differential across thejet system I2 is a measure of the rate of flow of fuel'thru that'system. The fuel pressure upstream from the jet system I2 is communicated thru a conduit. I to the chamber 50 in pressure meter 40. The fuel pressure downstream from the jet system I2 is communicated thru a conduit I28 to the chamber 58 in the pressure meter 40. Since the pressure upstream from the jet system is the greater of the two, it may be seen that this fuel pressure differential acts on the valve stem 60 in a valve closing direction.

The'air pressureupstream from the restriction 28 in the secondary air passage previously described is communicated thru a conduit I to the chamber 52 in the pressure meter 40. The pressure downstream from restriction 28 in the secondary air passage is communicated thru a con- The conduit. 86 conducts the fuel either thru a fixed metering restriction or jet 90,'-or thru a restriction 92 controlled by a valve 94 biased to closed position by a spring 96. The conduit 88 conducts fuel thru a flxed restriction 98. Fuel I 62 pivctally attached to a lever I04, whose opposite end is connected by a link I05 to an arm I68 fixed on the shaft H0 of the throttle I6. The idlevalve is normaly wide open when the throttle is beyond a range of positions near its closed posi-. tion, usually termed the idling range. As the throttle moves into the idling range, thereby decreasing the air flow, the idle valve I02 moves toward closed position.

The flow regulator I8 includes apair of expansible chambers I I2 and H4 separated by a'flexible diaphragm I I6, which is attached at its center to a valve II8. A spring I20 biases the valve The chambers II2 and I I4 are connected by a restricted passage I22. The chamber I I2 is also connected thru a conduit I24 to the valve chamber 52 of pressure meter 4B. The flow of fuel into valve chamber 62 mm ,duit I32 to chamber 56 of the pressure meter 40.

Since the pressure upstream from restriction 28 is greater than the downstream pressure, it must beseen that this air pressure differential acts on the valve stem 60 in a valve opening direction.

The valve'stem' and hence the-pilot valve 64 are therefore positioned by the difference between two opposing forces, one proportional to the fuel pressure differential and hence the fuel flow, and

acting on the valve in a closing direction, and

the other proportional to the air flow and acting on the valve in an opening direction. A spring is also provided which biases the valve 64 for movement in an opening direction.

The chamber II2 of the flow regulator I8 receives fuel thru the'restri'cte'd passage I 22, and fuel is discharged from chamber II2 thru the valve 64. The pilot valve 64 therefore controls the pressure in chamber II2, and thereby the opening of the main valve I I8 and hence the rate of flow of fuel thru the carburetor.

, Operation I The rate of flow of air thru the air conduit I0 ""is determined chiefly by -the position of the throttle and by the speed of the engine. As the air flows thru the conduit III, a pressure differential is produced across restriction 28 which is a measure of that airflow. This pressure differential acts in an opening direction on valve stem 60 and pilot valve 54, so that the valve 54 starts to open and continues its opening movement until that movement is arrested by the application of an equal and opposite force in a closing direction by the fuel pressure differential across the jet system, which is applied to chambers 50 and 58 of the pressure meter 40. As the pilot valve 64 is moved towardopen position, the pressure in chamber II2 of flow regulator 18 is reduced. Since the pressure in chamber II4is'higher than the pressure in chamber II2, due to the restriction in passage I22, 9. reduction of the pressure in chamber 1 I2 cause's'the main valve I I8 to move toward open position, thereby increasing: the fuel flow. This increasein the fuel flow continues until the force applied to valve stem 60 by the fuel pressure differential equals the opposite force applied by the air pressurediiferential. Movement of valves 60 and I I8 then stops, and the fuel flow is established-at a value proportional to the airflow. I

If the fuel flow is too .great for the air flow,

' valve 64 is substantially unaffected by varlations inthepressure in chamber H2, which is controlled by valve 64. Therefore, the'valve N moves only when the fuel and air differential pressures are unbalanced, and continues to move until they are balanced or until the valve 64 reaches its limit of movement. l5

'For example, if the air flow increases; causing valve 64 to open, but the main valve H8 sticks, so that the fuel flow does not increase, then the valve 64 continues to move until it is open wide, unless the valve H8 is first loosened by the increasing pressure differential acting on diaphragm H4. When valve 64 is wide open, the pressure differential acting on diaphragm, H4 is substantially the full pressure drop existing between chamber HI and the main air passage. sticks on a decreasing air flow, the valve 64 will close completely, so that there is then no pressure differential acting on diaphragm H4, and the full force of spring l 20 is brought into play to unstick the valve.

Therefore, the full force of the total pressure differential between chamber H4 and air passage I2 is always available to move the main valve in one direction, and the full force of spring 120 is always available to moveit in the other direc- 36 tion. The force applied to move the valve is limited only by the force available, and not by the magnitude of the unbalance between the air and fuel pressure differentials.

When the throttle is in the idling range of 4,0

' positions near its closed position, the air pressure differential is so small thatit does not provide an accurate measure of the rate of flow of air. At this time, the spring 65 is the predominating force acting in an-opening direction on valve 64. Since the'force of spring at this time is greater than that due to the air pressure differential, the valve 64 is opened wider than is indicated as necessary by the airpressure difal. Th valve H8 is likewise o ened wider, r ferenu e p pressure in said second conduit, said wall being due to the reduction in pressure in chamber H2. At this time, the idle valve I02, which is linked to the throttle I6, is moved toward closed position, thereby reducing the fuel'flow. The effect of spring 65 is to remove the air pressure dif- 55 ferential from the control of the fuel fiow when that air pressure differential falls too low. The fuel fiow is at that time controlled by the idle valve I02, since it has been foundthat the throttle controlled idle valve I02 is much more reliable Q as a fuel flow control at low air flows.

' When the valve 82 of the mixture control 0 is movedfrom the ,full line position indicated in the drawing to the dotted line position, the crosssectional area of the path thru the jetsvstem 12 open to the flow of fuel is increased. This increases the rate of fuel flow obtained for a-given value of the fuel pressure differential. Therefore, the carburetor controls the fuel supply to provide an enriched fuel-to-air ratio when the mixture control valve 82 is in its dotted line position.

Likewise, the opening of the valve '94 in response to a high fuel pressure differential increases the cross-sectional area of the fuel flow path thru the jet system l2, and thereby in- 76 If the valve, H8 35- creases the fuel-to-air ratio. This enrichment at high air flows is provided to prevent detonation at high engine power outputs, and to enable the engine to run cooler under such conditions.

. It may be observed that inthefuel line in my carburetor there are only two substantial pressure drops, one in the jet system 12 and one thru the valve H8. Since; havereduoed the number of pressure drops to a minimum, I have reduced the total over-all pressure drop and thereby the tendency of the fuel to vaporize in the fuel line. Also, since the first pressure drop is thru the metering orifices or jetatheabsolut pressures on both sides of these jets are as high as possible consistent with given conditions. as to inlet pressure and pressure drop thru the jets. Therefore,

, the tendency of the fuel to vaporize in the jets,

where such vaporization might cause serious errors in the fuel metering, is minimized.

It shouldalso be noted that the pressure meter 40 may be used with any size of carburetor. The dimensions of the air venturi l4 and the fuel jet system 12.,might have to be varied to suit the capacities of different engines, but any given size of pressure meter 40 could be used on any size air and fuel supply system.

While I have shownvland described a preferrpd embodiment of my invention, other modifications thereofwill readily occur to those skilled in the ated with said first conduit for producing two unequal air pressures whose difference is a measure of the rate of flow of air thru said conduit,

means for supplying fuel under superatmospheric pressure, a second conduit for conveying fuel from said fuel supply means to said engine, a metering restriction in said second conduit effective to control the flow of fuel therethru as a function of the fuel pressure differential thereacross, a main valve for variably restricting said second conduit to control the flow of fuel therethru, an'expansible' chamber having a movable wall subject on its exterior surface tothe fuel operatively connected to said main valve for positioning the same, a restricted inletpassage conv necting the interior of said chamber t said second conduit, a restricted outlet passag connecting the interior of said chamber to a point maintained at a continuously lower pressure, a pilot valve for controlling one of said restricted passages, a stem for said valve, a rigid wall for said acted on by the pressure in said one passage being negligibly small as compared to the area of said air pressure difference responsive means,

so that said valve is positioned in response to said air pressure difference and substantially inde-- pendently of the pressure in said one passage.

2. A fuel and air proportioning device for an internal combustion engine, comprising in combination, a first conduit for conveying air for combustion purposes to said engine, means associated with said first conduit for producing two 7 unequal air pressures whose difference is a measure of the rate of flow of air thru said conduit, means forsu'pplying fuel under superatmospheric pressure, a second conduit for conveying fuel from said fuel supply means to said engine, a metering restriction in said second conduit effective to control the flow of fuel therethru as a function of the fuel pressure differential thereacross, a main valve for variably restricting said second conduit to control the flow of fuel therethru, an expansible chamber having a movable wall subject on its exterior surface to the fuel pressure in said second conduit, said wall being operatively connected to said main valve for positioning the same, a restricted inlet passage connecting the interior of said chamber to said second conduit, a restricted outlet passage connecting the interior of said chamber to a point maintained at a continuously lower pressure, a pilot valve for controlling one of said restricted passages, a stem for said pilot valve, a rigid wall for said one passage, said rigid wall being apertured to permit passage of said stem therethru, and means acting on said stem outside said wall to position said pilot valve in response to the balance between the difference of said air pressures and said fuel pressure differential, the unbalanced area of said pilot valve acted on by the pressure in said one passage being negligibly small as compared to the area of said balance responsive means, so that the pilot valve is positioned in accordance with'said balance and substantially independently of the pressure in said one passage, whereby a change in said difference of air pressures causes movement of said pilot valve either until said fuel pressure differential is changed to balance the change in air flow or until said pilot valve reached its limit of movement.

3. A fuel and air proportioning device for an internal combustion engine, comprising in ,combination, a first conduit for conveying air for combustion purposes to said engine, means associated with said first conduit for producing two unequal air pressures whose difference is a measure of the rate of flow of air thru said conduit for conveying fuel from said fuel supply means to said engine, a metering restriction in said second conduit effective to control the flow of fuel therethru as a function of the fuel pressure differential thereacross, a main valve for variably restricting said second conduit to control the fiow of fuel therethru, an expansible chamber having a movable Wall subject on its exterior surface to the fuel pressure in said second conduit, said wall being operatively connected to said main valve for positioning the same, a restricted inlet passage connecting the interior of said chamber to said second conduit, a restricted outlet passage connecting the interior of said chamber to a point maintained at a continuously lower pressure, a

pilot valve for controlling said restricted outlet passage, a stem for said pilot valve, a rigid wall for said outlet passage, said rigid wall being apertured to permit passage of said stem therethru, and means acting on said stem outside said wall to position said pilot valve in response to the balance between the difference of said air pressures and said fuel pressure differential, the unbalanced area of said pilot valve acted on by the pressure in said one passage being negligibly small as compared to the area of said balance responsive means, so that the pilot valve is positioned in accordance with said balance and substantially independently of the pressure in said the air flow increases, the pilot valve continues to open until the full pressure differential between said conduit and said lower pressure acts on said wall to move said main valve.

4. A fuel and air proportioning device for an internal combustion engine, comprising in combination, a first conduit for conveying air for combustion purposes to said engine, means associated with said first conduit for producing two unequal air pressures whose difference is a measure of the rate of flow of air thru said conduit, means for supplying fuel under superatmospheric pressure, a second conduit for conveying fuel from said fuel supply means to said engine, a metering restriction'in said second conduit effective to control the flow of fuel therethru as a function of the fuel pressure differential thereacross, a main valve for variably restricting said second conduit to control the flow of fuel therethru, an expansible chamber having a movable wall subject on its exterior surface to the fuel pressure in said second conduit, said wall being operatively connected to said main valve for positioning the same, a restricted inlet passage connecting the interior of said chamber to said second conduit, a restricted outlet passage connecting the interior of said chamber to a point maintained at a continuously lower pressure, a spring acting on said wall in opposition to the difference between the pressure in said conduit and the pressure in said chamber, a pilot valve for controlling one of said restricted passages, a stem for said pilot valve, a rigid wall for said one passage, said rigid wall being apertured to permit passage of said stem therethru, and means acting on said stem outside said wall to position said pilot valve in response to the balance between the difference of said air pressures and said fuel pressure differential, the unbalanced area of said pilot valve acted on by the pressure in said one passage being negligibly small as compared to the area of said balance responsive means, so that the pilot valve is positioned in 4 accordance with said balance and substantially independently of the pressure in said one passage, whereby if said main valve sticks, either the full pressure differential between said conduit and said lower pressure, or the full force of said spring, is available to act on said wall and move said main valve.

5. A fuel flow controlling device for an internal combustion engine,comprising means for producing a force varying in accordance with the power output of said engine, a conduit for conveying fuel to said engine, a metering restriction in said conduit effective to control the flow of fuel therethru as a function of the fuel pressure differential thereacross, a main valve for variably restricting said conduit to vary the fiow of fuel therethru, an expansible chamber having a movable wall subject on its exterior surface to the fuel pressure in said conduit, said wall being operatively connected to said main valve for positioning the same, a restricted inlet passage connectingthe interior of said chamber to said conduit, a restricted outlet passage connecting the interior of said chamber to a point maintained at a continuously lower pressure, a pilot valve for controlling one of said restricted passages, a stem for said pilot valve, a rigid wall for said one passage, said rigid wall being apertured to permit passage of said stem therethru, and means acting on said stem outside said wall to position said pilot valve, said pilot valve posiential is changed to balance the change in power output or until said pilot valve reaches its limit of movement.

. PAUL F. ADAIR.

REFERENCES CITED 'The following references are of record in the file of this patent:

UNITED PATENTS Date 10 Number I Name 2,283,921 Udale May 12, 1942 2,316,300 Udale Apr. 13, 1943 2.341357 Wunsch Feb. 8, 1944 2,848,008 Hunt May 2, 1944 

